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The influence of a Jahn-Teller ion on magnetization,g-values and linewidth in ZnxFe3−xO4and Ni1−xZnxFe2O4spinel ferrites has been investigated by introducing small quantities of Cu2+ions. The magnetization of Cu substitution in both the systems but the curie temperature is affected only in FeZn ferrites. The lattice constant in NiZn is significantly reduced while in FeZn there is only a slight increase. The change ingeffon copper substitution,Δgeff, is very different in the two systems. In NiZn,Δgeffhas a uniform value, ∼ 0·2, for all values ofxwhile in FeZn it has a peak atx=0·3 and vanishes atx=0 andx⩾0·5. The ferromagnetic linewidthΔH does not change significantly on copper substitution in both the systems. An explanation based on the perturbation produced due to the local lattice distortion by the Jahn-Teller mechanism explains the observed results satisfactorily.

The presence of small amounts of Fe2+ion in nickel zinc ferrite significantly influences some of its magnetic properties. The lattice parameter increases slightly and the increase Δais independent ofx. The variation of magnetization with zinc concentration is explained on the basis of the Yafet-Kittel model. Increase in the Néel temperature on Fe2+substitution in ZnxNi1-xFe2O4is remarkable. This has been explained on the basis of a four sublattice model. Our analysis shows thatJAB(d5-d5) interaction is most affected. The influence of Fe2+ions on the relaxation processes in the Mössbauer line shapes of Ni-Zn ferrite is also investigated and is compared with Cu2+doped Ni-Zn ferrite.